FIG. 1 is a perspective of a conventional RF modulator, reference numeral 11 being an antenna's input port and 12 being an RF signal output port given to a TV set.
FIG. 2A is a block diagram of the conventional RF modulator, and FIG. 2B is a circuit diagram of mixer 23 shown in FIG. 2A. Referring to FIG. 2A, the RF modulator includes an amplifier 21 for amplifying a telecast RF signal input through ANT input port, a modulation section 22 for modulating RF signals of video cassette recorder (VCR), satellite video receiver (SVR), or game player, and a mixer 23 having an RF output tap and for mixing the first RF signal RF1 output from amplifier 21 and the second RF signal RF2 output from modulation section 22 into a third RF signal RF3 which is then provided to a TV set through the output tap. In FIG. 2B mixer 23 is made with a mixer transformer T21 which mixes the first RF signal RF1 output from amplifier 21 and the second RF signal RF2 output from modulation section 22 into a third RF signal RF3.
According to the prior art, one RF modulator enables only a single not multiple TVs to be viewed. Several TVs can be viewed simultaneously with several RF modulators connected in parallel. However, in this case the RF modulators occupy much volume, and their mounting is not so easy, decreasing economic efficiency as well.